When solving static or quasi-static type problems, the default Implicit Static solver (IMAS=0 in CONTROL_IMPLICIT_DYNAMICS) requires a well-conditioned model, with no rigidbody modes, to get good convergence behavior. It is often difficult to prevent rigidbody modes especially when its dependent on contact-impact conditions. In such cases, use of Implicit Dynamics solver (IMAS=1) can help us to achieve better convergence since rigidbody modes has negligible effect on the convergence. In versions prior to 971 (revision 3), when IMAS=1, LS-DYNA included dynamic terms for the entire duration of the problem. Consequently, when using the implicit dynamics solver for solving static or quasi-static problems, the loading rate would have be reduced substantially to reduce the dynamic effects. Starting from 971 (revision 3), LS-DYNA now allows birth, death and burial times for the implicit solver which can be used to control the presence of the dynamic terms without altering the loading rate. TDYBIR (default =0) can be used to activate the dynamic affects. TDYDTH (default = 1e28) allows to specify a death time when the dynamic terms must be ignored. The parameter TDYBUR (default = 1e28) allows to specify a burial time (must be greater or equal to the death time) which if greater than the death time, the dynamic effects are linearly reduced to zero from death to burial time. Graphically, it can be represented as shown below (The following image has now been included in the latest LS-DYNA User’s Manual).

(Click image to enlarge)